Integrated circuit connection devices are known in the prior art. Indeed, integrated circuits are generally fitted with connection devices enabling the connection of external components and communication between the external element and said integrated circuit.
These connection devices consist of two active MOS (PMOS and NMOS) transistors in an inverter arrangement to form a buffer. Thus the gates of the two transistors, forming the inverter input, are connected to the supply voltage and earth of the integrated circuit. The transistors drains, forming the inverter output, represent the external contact pad across which an external component will be connected.
One problem of these connection devices is that only components whose voltage level is lower than or equal to the voltage applied to the gate of the MOS transistors can be connected. In other words, the operating voltage of the external components must not be higher than the integrated circuit supply voltage. However, the object of this type of connection device is for the PMOS transistor of the buffer to always be non-conductive while the voltage applied across the drains is lower than the voltage applied across the gates.
Indeed the buffer is always non conductive as long as the voltage of the connected external component is lower than or equal to the gate voltage which is generally close to the supply voltage. If an external component whose operating voltage is higher than the PMOS transistor gate voltages is connected, the buffer is liable to no longer be non conductive.
Buffer conductivity can cause a current increase in the PMOS transistor of the inverter. This can lead to a current injection from the external component into the integrated circuit supply voltage. This current injection then introduces noise in the supply voltage and excessive power consumption.
Moreover, the current tendency in electronics is to reduce circuit supply voltages. This tendency is incompatible with having external component operating voltages that are lower than or equal to the MOS transistor gate voltages.
Integrated circuit connection devices that have a protection system if the voltage applied to the contact pad is higher than the operating voltage of said circuit are also known from U.S. Pat. No. 5,574,389.